Flaw detector system utilizing a laser scanner

ABSTRACT

A laser beam is scanned successively across a surface of material being analyzed, and the intensity of the beam, either reflected or transmitted from the material, is detected by a photomultiplier tube. In addition to output amplitude, variations due to scanning across material flaws, other photomultiplier output variations also occur. Such baseline variations are due to relative angle changes that occur between the laser beam and the material surface and other system-associated errors. The same optical and/or electrical variations that produce these baseline signals also cause corresponding amplitude variations of detected flaw signals. A flaw amplitude normalizer circuit is coupled to the detector for automatically normalizing the flaw signal to remove these errors by providing high and low-pass filters to separate the flaw signal from the baseline scanning signal, and these signals are ratioed to develop a normalized flaw signal. A threshold circuit is coupled to the flaw amplitude normalizer circuit for producing flaw output signals when the normalized flaw signals from the detector exceed a predetermined level. Outputs from the threshold circuit are applied to a flaw quantizer circuit which, using &#39;&#39;&#39;&#39;0-1&#39;&#39;&#39;&#39; logic to indicate a flaw area and discriminate against the same indication on successive scans which occur at the same position in the scan as the initial flaw indication, thus provides a single flaw indication for the same flaw, although it may occur on successive scans.

United States Patent Baker Dec. 25, 1973 FLAW DETECTOR SYSTEM UTILIZINGA LASER SCANNER [75] Inventor: Cole H. Baker, Westport, Conn.

[73] Assignee: Intec Corporation, S. Norwalk,

Conn.

[22] Filed: June 23, 1972 [2]] Appl. N0.: 265,614

[52] US. Cl 235/l51.3, 250/219 DF [51] Int. Cl. Gln 21/32 [58] Field ofSearch 235/1513, 151.35; 250/219 DF, 219 WE, 219 D, 219 QA, 219 Q, 219R, 217 R, 217 SS; 340/347 CC [56] References Cited UNITED STATES PATENTS3,026,415 3/1962 Lake, Jr. et a1. 250/219 DF X 3,652,863 3/1972 Gaskellet al 250/219 DF 3,061,731 /1962 Thier et a1. 250/219 DF 3,534,40210/1970 Crowell et a1... 235/1513 X 3,586,864 6/1971 Brany et a1.250/219 DF Primary Examiner-Joseph F. Ruggiero Att0rneyJoseph Levinson[57] ABSTRACT A laser beam is scanned successively across a surface ofmaterial being analyzed, and the intensity of the beam, either reflectedor transmitted from the material, is detected by a photomultiplier tube.ln addition to output amplitude, variations due to scanning acrossmaterial flaws, other photomultiplier output variations also occur. Suchbaseline variations are due to relative angle changes that occur betweenthe laser beam and the material surface and other system-associatederrors. The same optical and/0r electrical variations that produce thesebaseline signals also cause corresponding amplitude variations ofdetected flaw signals. A flaw amplitude normalizer circuit is coupled tothe detector for automatically normalizing the flaw signal to removethese errors by providing high and low-pass filters to separate the flawsignal from the baseline scanning signal, and these signals are ratioedto develop a normalized flaw signal. A threshold circuit is coupled tothe flaw amplitude normalizer circuit for producing flaw output signalswhen the normalized flaw signals from the detector exceed apredetermined level. Outputs from the threshold circuit are applied to aflaw quantizer circuit which, using 0-1 logic to indicate a flaw areaand discriminate against the same indication on successive scans whichoccur at the same position in the scan as the initial flaw indication,thus provides a single flaw indication for the same flaw, although itmay occur on successive scams 7 Claims, 14 Drawing Figures PIPE-AMP J T22 EUFFEI? FLAWPASS 3 j l COMPARATOR I 6 550L075 H 20 FILTER II VALUE 5I I I I AMP l 44 36 3a /4 SCAN II I EASE L/NE ANALOG I l PASS F/L TEEMUL T/PL IE? 42 TFL AW AMPL TUEAEHWL lZER B/ll/A/PY COUNTEI-r H r I I ll I l l 05c. FREQUENCY I o/v/om CHA/A/ FLOP I 60 aa/r /023 5/7 5 SHIFTSHIFT L I L REG. REGISTER 6A I CL 44 0 1| CL I I ll 1 IL fwfl L E J l 50I SYSTEM 5YA/CHRO/V/ZER\ I F LAW DETECTOR SYSTEM UTILIZING A LASERSCANNER BACKGROUND OF THE INVENTION This invention relates to a flawdetection system, and more particularly to such a system utilizing alaser scanner which is capable of detecting flaws which might otherwisebe missed due to signal variations caused by scanning or system changesin signal level. The flaw detection system further includes means forpreventing multiple flaw indications of a single flaw which is producedby successive scans of the same flaw.

In the manufacturing process, certain surface flaws will from time totime occur even with the most rigid quality control program. Thesurfaces in which the flaws occur may be in the form of a continuousmoving web of material, such as paper, film, plastic, etc., or invarious piece parts of similar or different materials. Visual inspectionby trained operators is both costly and inaccurate, particularly withrespect to high speed production of continuously moving webs ormaterial, or where the number of parts to be examined visually isprohibitive. Accordingly, flaw detection systems have been widelyemployed to monitor the inspection of materials for flaws. Laser scannersystems have been widely used, which apply a flying spot of highintensity light which is repetitively scanned across a moving sheet orpiece part with light being reflected therefrom, to be received by aphotomultiplier detector. If the material is translucent, the light maybe directed through the material, and analyzed by the photomultiplier.Accordingly, at any instant of time during the scan, the photomultiplieroutput is proportional to the reflectiv ity or transmissivity of thespot upon which the laser beam is impinging. Flaws occurring on thesurface of the material being examined change the output of thephotomultiplier tube due to the reflective or transmissive properties ofthe material being examined, providing a means for indicating flaws onthe surfaces. Generally, flaws are relatively small and flaw signalsgenerated therefrom are usually of a much shorter time duration ascompared to a single line scan cycle across the material. By means offrequency or time selective filtering, the short-duration flaw signalpulsescan be separated and distinguished from the lower frequencycomponents generated by the baseline scan. By processing the flawsignals through appropriate threshold circuitry, the flaw signals can becategorized in regard to amplitude, duration, and/or polarities.

When scanning across homogeneous flaw-free surfaces, a certain quantityof reflected or transmitted light is seen by the photomultiplier,producing a light level which is referred to as the baseline signal. Asstated previously, the light level will increase or decrease from thebaseline level as a result of a flaw in the surface of material beingscanned. One of the problems involved with such systems is that theamount of light impinging on the surface of the photomultiplier whenscanning flaw-free material is that this level does not remain constant.This light level varies as a function of the impingement angle of thelaser beam on the material being scanned, as well as the relative anglesand distances between the laser beam and the photomultiplier.Additionally, the type of surface being examined also affects the amountof light impinging on the photomultiplier. Furthermore, changes in thecharacteristics of the optical and electrical apparatus with age and/oruse change the signal level which will be produced by thephotomultiplier tube even though it is not scanning a flawed area. Theproblem of the changing baseline signal when no flaws appear on thesurface increases the difficulty in flaw detection, where some flaws aremissed entirely, and other flaws are indicated where none exist.

' One approach to the problem of changes in flaw signal amplitudeassociated with the relative position of the laser beam during a normalscan cycle involves optically compensating the relative light levelreceived by the photomultiplier as a function of the scan angle. Avignetting mask was used to reduce the light reflected from the sheet tothe photomultiplier tube at those scan angles which produced larger flawsignals than other scan angles, and to increase the light falling on thephotomultiplier for smaller flaw signals which were such due solely tothe scan angle. The vignetting mask was then empirically adjusted forall other in-between scan positions to provide a normalized flaw outputsignal where equal size and type flaws would presumably produce an equalsignal, irrespective of its location along the scan line. However, thevignetting mask technique is difficult to implement, and variations ofthe material surface characteristics, as well as any changes in thelaser-to-material scan angle or relative photomultiplier position,necessitate a complete reshaping of the vignetting mask. Furthermore,there is no way to implement an automatic operation for such changes.

Another drawback of prior art flaw detection systems utilizing laserscanners involves repetitively seeing the same flaw on successive scans,and producing false multiple-flaw indications where only the firstindication is desired. Prior flaw detection systems count the same largeflaws many times, while even minute flaws produce multiple'counting ifthe scanning speed is slow enough. Also, extended flaws which vary aslight angle with the direction of surface travel have been multiplycounted where only a single flaw existed.

Accordingly, it is an object of this invention to provide a new andimproved flaw detector system which overcomes some of the aforesaidproblems associated with prior art systems.

A further object of this invention is to provide a new and improved flawdetection system utilizing a laser scanner which is capable of detectingflaws in surfaces of material regardless of the position of the flaw onthe material being scanned.

A still further object of this invention is to provide a new andimproved flaw detector system which automatically compensates forscanning and system error, thus providing a greater capability fordetecting flaws.

Another object of this invention is to provide a new and improved flatdetection system which provides a single flaw indication for acontinuous flaw which covers successive scan lines even when such flawis slightly skewed to the direction of scanning on the surface of thematerial being analyzed.

SUMMARY OF THE INVENTION In carrying out this invention in oneillustrative embodiment thereof, a laser beam is successively scannedacross a surface of material being analyzed, and a detector means ispositioned for receiving radiation applied by the laser beam from thesurface for producing a signal in response to the intensity of theradiation received. A flaw-amplitude analyzer circuit is coupled to thedetector for automatically adjusting flaw signal amplitudes along thescan lines such that flaws of similar characteristics have the sameamplitude no matter where they are positioned along the scan line. Athreshold circuit is coupled to the flaw amplitude normalizer circuitfor producing a flaw signal output when such signals exceed apredetermined level, which signals are applied to a flaw quantizercircuit which counts single flaws along the surface being scanned anddiscriminates against the same flaw signal which appears in successivelyscanned lines.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic block diagramillustrating a preferred embodiment of the improved flaw detectorsystem.

FIGS. 2-13 show wave forms which are used to illustrate the operation ofthe flaw detector system shown in FIG. 1.

FIG. 14 is a schematic block diagram of another embodiment of a flawamplitude normalizer circuit which may be utilized in the system shownin FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention isdescribed and illustrated using a moving sheet or web of material, withthe detector positioned to receive the reflected light from suchmaterial. It should be understood that the invention is equallyapplicable to flaw detection of piece parts or devices whose surfacesare to be examined for defects in which such parts move along a conveyoror other suitable means. The parts may also be stationary and thescanning done in raster form by known methods. If the materials beingexamined are translucent, the system would also be applicable formeasuring the light transmitted through the material for flaw detectioninstead of the use of reflected light as shown.

Referring now to FIG. 1 of the drawings, a conventional laser of anysuitable type, such as heliumneon or argon ion gas lasers, or othertypes which are capable of generating a laser beam of monochromaticlight in a predetermined spot size, is scanned by a galvanometer mirror14 successively across a web of material 15 which is continuously movingin the direction shown. Scanning across the web is achieved by using anoscillator 24 in the flaw system synchronizer 25 which feeds a binarycounter frequency divider 26 to produce at its output a signal ofwaveform A shown on FIG. 2 which for purposes of illustration may be 1khz. Waveform A is applied to a galvanometer driver 16 whose outputwaveform C is shown in FIG. 4 in the form of a synchronous triangulardrive waveshape which is applied to and powers a high speed galvanometer12. The mirror 1 on the galvanometer 12 reflects the laser beam from thelaser 10 and causes it to scan back and forth across the surface of web15. Scanning in the orthogonal direction to create a raster is doneautomatically by the moving web 15. As is indicated on FIGS. 4 and 5,the laser beam scanning position, waveform D, time lags the galvanometerdrive, waveform C. A logic signal, waveform E in FIG. 6, is delayed by aflipflop circuit 28 which has waveform B of FIG. 3 (eg, 8 lghz) appliedthereto from the binary counter frequency divider 26 so that waveform Eis synchronous with the scan position of the laser beam, and its usagewill be covered hereinafter.

The laser beam scanning is generally perpendicular to the direction ofthe web motion to provide complete coverage of the surface of the web 15as the web 15 moves under the scanning beam. Light reflected from thesurface of the web 15 is received bya detector such as photomultipliertube 20, the output of which is amplified in a preamplifier 22 and shownas waveshape F in FIG. 7. The waveform F consists of a baseline signalassociated with scanning the surface of web 15 whether any flaws existor not. It will be noted in the particular example that the baselinesignal is greater near the center of the web and tapers off at theedges. Any flaws which exist in the surface of the web 15 will produceflaw signals at the output of the photomultiplier 20 which aresuperimposed on the baseline signal. The flaw signals are short durationpulses that correspond to scanned flaws which are shown in waveform F ofFIG. 7 as different amplitude positive and negative signalscorresponding to the type of flaw which is detected. The flaw amplitudeof the waveform F is a combined function of the magnitude of the scannedflaws as well as their position along the scan line.

The output of the preamplifier 22 in the form of waveform F is appliedto a flaw amplitude normalizer circuit 30 whose function is tonormalize, or even out, the varying baseline signal due to scanning andother system errors. Waveform F is applied to a buffer amplifier 32. Theoutput of the buffer amplifier 32 is applied to two channels, first aflaw-pass filter 34 which is in the nature of a high pass filter andpasses only the short duration flaw signal pulses, and thus separatesthem from any residual scan signals. In the other channel, the waveformF signal is applied to a scan baseline filter which is a low-pass filter36 for passing the lower frequency baseline scan signals and blockingthe higher frequency flaw signals. The output of the scan baselinefilter 36 is applied to one input of an analog multiplier 38. The outputof the flaw-pass filter 34 in the form of flaw signals is applied to anoperational amplifier 40 whose output is applied via a feedback path 42to the other input of the analog multiplier 38. The output of the analogmultiplier 38 is connected to the other input of the operationalamplifier 40. In view of this negative feedback arrangement, the outputof the operational amplifier 40 driving the input of the analogmultiplier 38 which in turn drives one of the inputs to the operationalamplifier 40, the non-normalized flaw signals produced at differentpoints along the scan line are divided by the baseline signal levelpresent at the corresponding positions along the scan line. Thisratioing of the flaw signals and the baseline signals results in theautomatic normalizing of flaw signal amplitudes and is shown in FIG. 8as waveform G which appears at the output of the flaw amplitudenormalizer 30.

It should be noted that the flaw amplitude normalizer circuit 30 alsoeliminates flaw signal amplitude variations that occur due to causesother than those associated with purely scanning. If surfacereflectivity, laser light output, or photomultiplier and its associatedamplifier gain changes occur, such changes would also affect the flawoutput signal levels. In such a case, baseline signal levels wouldincrease and decrease proportionately with such signal level changes.However, the ratioed flaw-signal-to-baseline-signal amplitudes wouldremain unchanged due to the flaw amplitude normalizer cirucit 30. Thisself-adjusting feature eliminates the need for trimming to accommodatelong-term gain variations within the system.

Waveform G is fed from the flaw amplitude normalizer circuit 30 to athreshold circuit 45 which accommodates both positive and negative flawoutput signals. Waveform G is applied to an absolute value amplifier 44which full-wave rectifies the normalized flaw signals of waveform G,producing waveform H shown in FIG.

' 9. Waveform H is applied to a comparator 46 having a predeterminedthreashold level set by a potentiometer 48. Accordingly, flaw pulseswhich exceed the predetermined threshold of comparator 46 produce a (lllogic drive signal of waveform I shown on FIG. 10. These logic signalscontained in waveform I are applied to a flaw quantizer circuit 50.Thus, the threshold circuit 45 produces repetitive output pulsescorresponding to successive scans passing along any single flaw that maybe present on the surface of the material 15. The purpose of the flawquantizer circuit 50 is to pass only the first pulse produced, and toreject any subsequent flaw pulses that occur at the same scan positionduring adjacent successive scan intervals.

The input of the flaw quantizer circuit 50 is comprised of a gate 52which is fed at one input thereto from the threshold circuit 45 and atthe other input thereto from a clear signal generator 23 applied throughan amplifier 27. The purpose of the' clear signal generator 23 is to setthe logic of the quantizer 50 for a complete scan interval. This may bedone manually, as would be the case for a moving web such as 15, or itmay be done automatically, utilizing a sourcephotodetector combinationto monitor and detect the edge of the piece part which is being scanned.The gate 52 is connected ta five-bit shift register 54 which is coupledto a NOR gate 56, and from there toa 1,023-bit shift register 58. Theoutput of the l023-bit shift register 58 is applied to a flaw gate 60whose output corresponds to the quantized flaws. The flaw quantizer 50is also fed with synchronized delayed clock pulses from the oscillator24 of the system synchronizer 25 through its output AND gate 29. Theoutput of the gate 29 is coupled to both shift registers 54 and 58.

In operation, a clear signal is applied from clear signal generator 23just prior to initiating the quantizer operation for the time durationof a complete scan interval. The clear signal causes a logic input levelto be applied to the serial input of the five-bit series-toparallelshift register 54. During the scanning interval corresponding to thedelay l-khz signal (waveshape B being at logic 1), high frequency clockpulses are gated by the AND gate 29 from the oscillator 24 into the flawquantizer circuit 50 These pulses which are applied to the shiftregister 54 shift the input clear logic 0 signal into the five-bit shiftregister 54, causing the output of the five-input NOR gate 56 to go tothe logic 1 level. In turn, subsequent clock pulses cause logic 1signals to be entered into all the stages of 1,023-bit shift register58. At the termination of the clear signal, one input to the flaw ANDgate 60 will be at logic 1 level (1,023-bit shift register output 58)and the other input (bit 3 of the five-bit shift register 54) will be atthe 0 logic level. Simultaneously, the AND gate 52 at the input of theflaw quantizer 50 will be enabled, and any subsequent threshold flawsignals will be transferred to the five-bit shift registers serial inputterminal.

Whenever the l khz delayed signal waveform E is at 1 logic, scanningacross the material is being effected in one direction, and wheneverthis signal is a 0 logic,

which is the reverse direction, retrace scanning is occurring. Duringthe logic 1 intervals, clock pulses from the system synchronizer 25causes any threshold flaw signals to be transferred into and through thefive-bit shift register 54. The first clock pulse subsequent to theappearance of the flaw signal transfers the logic flaw signal to thefirst shift register 54 output. This produces a logic 0 at the fiveinput NOR gate output, which in turn is transferred into the 1,023-bitshift register 58 on the next clock pulse. The third clock pulse causesthe flaw data to appear at the third place upward of the shift register54, and also produces a logic 1 at the output of the flaw gate 60. Theinput corresponding to waveform K of FIG. 12 is also at logic 1 becauseof the prior clear operation and the waveform L of FIG. 13 is producedat the output of the flaw gate 60.

Logic 1 level flaw data continues to be clocked into the five-bit shiftregister 54 until the termination of the flaw signal out of thethreshold circuit 45. Then logic 0 signals will be passed into andthrough the shift register until the next flaw signal again initiatesthe transference of logic 1 signals. During the time durationcorresponding to two clock pulses before, and two clock pulses after theflaw data appears at the three bit output of the five-bit shift register54 logic-0 signals are being entered into the 1,023-bit shift register58. During the first complete scan interval, subsequent to clearing theflaw quantizer 50, the 1,023-bit shift register is loaded with logic flsignals whenever flaw signals are detected. The logic 0 bit positions inthe register at the completion of the scan correspond to the flawpositions along the scan line. During the retrace interval, the clockpulses from the oscillator 24 are disabled, and the flaw position datais held in the register.

When the next scan interval occurs, logic 0 signals will appear at theoutput of the l,O23-bit register 58 in coincidence with the laser beamscanning across surface areas where flaws have previously been detected.In addition, the duration of logic 0s continues for five clock pulsessubsequent to the laser beam scanning past the area where previous flawswere detected. During the time intervals, when logic 0s appear at the1,023-bit shift register output, the flaw gate 60 blocks any flawsignals that may appear at the third place output of the five-bit shiftregister, and these flaw signals will not appear at the flaw gateoutput. Note that the stored data in the 1,023-bit shift registerstraddles the third bit output data by two bits. However, any new flawsscanned at other locations will still be passed through on this scan,and will be blocked on subsequent successive scans. Any perpendicularflaw stored at a corresponding position location will automatically becleared when a scan occurs that does not produce a flaw in that scanposition. Thus, as indicated by the waveform L of FIG. 13, only oneoutput pulse per flaw is produced at the flaw quantizer outputirrespective of the multiple scans occurring over the same flaw area.Because of the overlap provided by this arrangement, extended flaws thatare at some angle to the direction of the surface are also accommodatedand only counted as single flaws. Successive horizontal scans willproduce flaw signals positioned slightly before or after the immediatelyprior flaw signal. A false output would only result if the angle of theflaw is sufficient to produce an output pulse shifted in time by morethan two clock pulses during any two immediately successive intervals.If additional skew accommodation is desired, the five-bit shift registerlength can be increased. However, since extremely skewed flaws occurseldom in comparison with other types of flaws, the illustratedarrangement is deemed adequate to satisfy most requirements. In fact,for some applications, the five-bit shift register can be replaced witha three-bit register.

Another desirable feature of the flaw quantizer 50 is that it can beused to eliminate unwanted edge scanning signals that would appear aspulses at the output of the photomultiplier tube and would appear asflaw output signals if not eliminated. With the quantizer circuit 50,only during the first scan subsequent to clearing will edge over-scanproduce a flaw indication. On all subsequent overscans, the edge signalswill be blanked. Thus, by subtracting the initial overscan flaw count(maximum will be 2), the resulting flaw indications correspond only tothe actual flaws on the sheet. It is also possible to determine thelength or duration of a single flaw by the number of times such flaw isnot counted by the flaw quantizer 50.

FIG. 14 shows another embodiment of a flaw amplitude normalizer circuitwhich is useful for the system of FIG. 1 and the same elements andwaveforms will be designated with the same reference characters as thosein FIG. 1. The output of the preamplifier 22 is applied to the flawamplitude normalizer circuit 30 whose function is to normalize, or evenout, the flaw signals caused by the varying baseline of the signal, aspreviously explained. Waveform F is applied to a buffer amplifier 32.The output-of amplifier 32 feeds a flaw pass filter 34 which is ahigh-pass type filter for passing only short duration flaw signals to amultiplier circuit 62. The output of the buffer 32 also feeds the scanbaseline pass filter which is a low-pass type filter for passing thelower frequency baseline signal. The output of filter 36 is sent toanother multiplier circuit 64. Multiplier 64 in conjunction with anoperational amplifier 66 with the ap propriate feedback loop 68comprises a circuit which produces the reciprocal function of the inputbaseline signal. This reciprocal function is sent to the firstmultiplier 62 with the following result. The flaw signal passes throughthe flaw pass filter 34 and is multiplied by the reciprocal of thebaseline signal, thus normalizing or equalizing the flaw signal. Theoutput of the multiplier 62 is buffered by emitter follower 70 toprevent loading and slowing down the frequency response of the flawamplitude normalizer circuit 30. The output of the flaw amplitudenormalizer circuit 30 provides automatic normalization of the flawsignal amplitude as shown by waveform G of FIG. 8.

The advantage of the flaw amplitude normalizer circuit 30 of FIG. 14resides in the fact that the frequency response of the amplifier 66 usedto produce the reciprocal function need not be very wide. Also, thefrequency response of the normalizer circuit 30 is restricted only bythe multiplier 62 passing the highfrequency, short-duration flaws.

As illustrated in waveform H of FIG. 9, the system illustrated in FIG. 1does not provide polarity indications, but various modifications couldbe made to provide whatever additional information is desired. Forexample, it may be advantageous to know the quantity and polarity of theflaw, which information is contained in the normalized flaw signal ofwaveform G. Separate circuits such as routing circuits could be providedto direct flaws into appropriate counters to provide addi- All of theseflaw indications could be qualified by separate amplitude levels,tracking levels or equal amplitude levels which then might useindividual flaw quantizer circuits in accordance with the informationdesired to be extracted.

The above described flaw detection system employing the flaw amplitudenormalizer and flaw quantizer provide solutions to problems associatedwith laser scanning inspection of surfaces that previously either werenot solved or only partially solved in manners difficult to implement.This system may be utilized with a wide variety of materials and may beemployed for web-form surfaces or discontinuous surfaces, such as piecepart surfaces, without system degradation. Changes in the surfaces to beexamined, scanning angles and distances, and system gain changes due toaging, drift, etc., are all compensated for to enhance the flawdetection. Continuous, or slightly skewed continuous flaws are countedas single flaws, and edge pulses are effectively eliminated, utilizingthe same quantizer system. Although a digital mode is illustrated forthe quantizer system, an analog mode, such as delay lines, etc., couldalso be used.

Since other modifications, varied to fit particular operatingrequirements and environments, will be apparent to those skilled in theart, this invention is not considered limited to the examples chosen forpurposes of illustration, and covers all changes and modifications whichdo not constitute departures from the true spirit and scope of thisinvention.

I claim:

1. A flaw detection system utilizing a laser scanner for detecting flawson a surface of material, comprising a. a laser for emitting a beam ofradiation,

b. means for successively scanning said laser beam across a surface ofmaterial being analyzed,

0. detector means for receiving radiation applied by said laser beamfrom said surface producing a signal in response to the intensity of theradiation applied to said detector means,

d. flaw amplitude normalizer means coupled to said detector forautomatically normalizing flaw signal amplitudes which vary due toscanning and changes in the electrical characteristics of the systemcomprsing a high-pass filter for passing flaw signals from said detectormeans, a low-pass filter for passing scan baseline signals from saiddetector means, and means for ratioing said flaw signals with saidbaseline signals to normalize said flaw signals along the length of thescan line, and

e. threshold circuit coupled to said flaw amplitude normalizer means forproducing a flaw output signal when the signals from said detector meansexceed a predetermined level.

2. The flaw detection system set forth in claim 1 wherein said means forratioing said flaw signals with said baseline signals comprises ananalog multiplier circuit coupled to said low-pass filter, anoperational amplifier coupled to said high-pass filter and said analogmultiplier circuit, and means for coupling the output of saidoperational amplifier to the input of said analog multiplier circuit.

3. The flaw detection system set forth in claim 1 wherein said means forratioing said flaw signals with said baseline signals comprise an analogmultiplex circuit coupled to said high pass filter, means coupledbetween said low-pass filter and said analog multiplier circuit forapplying the reciprocal of said scan baseline signals to said analogmultiplier circuit whereby the output of said analog multiplier circuitprovides normalized flaw signals.

4. The flaw detection system of claim 1 including a flaw quantizercircuit coupled to said threshold circuit for passing an outputindicative of a flaw only on the first occurrence of a flaw signalduring a scan interval, and rejecting subsequent flaw signals duringadjacent successive scan intervals which occur at the same scanposition.

5. The flaw detection system of claim 4 wherein said flaw quantizercircuit comprises a. an adjustable delay means coupled to said thresholdcircuit for expanding said flaw signals from said threshold circuit,

b. scan interval delay means coupled to said adjustable delay means forproducing a delayed flaw signal approximately one scan interval aftersuch flaw signal is received from said threshold circuit, and

c. flaw gate means coupled to said scan interval delay means and saidadjustable delay means for passing an output indicative of a flaw onlyon the first occurrence of a flaw signal during a scan interval, andrejecting subsequent flaw signals during adjacent successive scanintervals which occur at the same scan position.

6. A flaw detection system utilizing a laser scanner for detecting flawson a surface of material, comprising a. a laser for emitting a beam ofradiation,

b. means for successively scanning said laser beam across a surface ofmaterial being analyzed,

0. detector means for receiving radiation applied by said laser beamfrom said surface producing a signal in response to the intensity of theradiation applied to said detector means,

d. threshold circuit means coupled to said detector means for producinga flaw output signal when the signals from said detector means exceed apredetermined level, and

e. a flaw quantizer circuit coupled to said threshold circuit forpassing an output indicative of a flaw only on the first occurrence of aflaw signal during a scan interval, and rejecting subsequent flawsignals during adjacent successive scan intervals which occur at thesame scan position.

7. The flaw detection system set forth in claim 6 wherein said flawquantizer circuit comprises a. an adjustable delay means coupled to saidthreshold circuit for expanding said flaw signals from said thresholdcircuit,

b. scan interval delay means coupled to said adjustable delay means forproducing a delayed flaw signal approximately one scan interval aftersuch flaw signal is received from said threshold circuit, and

c. flaw gate means coupled to said scan interval delay means and saidadjustable delay means for passing an output indicative of a flaw onlyon the first occurrence of a flaw signal during a scan interval, andrejecting subsequent flaw signals during adjacent successive scanintervals which occur at the same scan position.

1. A flaw detection system utilizing a laser scanner for detecting flawson a surface of material, comprising a. a laser for emitting a beam ofradiation, b. means for successively scanning said laser beam across asurface of material being analyzed, c. detector means for receivingradiation applied by said laser beam from said surface producing asignal in response to the intensity of the radiation applied to saiddetector means, d. flaw amplitude normalizer means coupled to saiddetector for automatically normalizing flaw signal amplitudes which varydue to scanning and changes in the electrical characteristics of thesystem comprsing a high-pass filter for passing flaw signals from saiddetector means, a low-pass filter for passing scan baseline signals fromsaid detector means, and means for ratioing said flaw signals with saidbaseline signals to normalize said flaw signals along the length of thescan line, and e. threshold circuit coupled to said flaw amplitudenormalizer means for producing a flaw output signal when the signalsfrom said detector means exceed a predetermined level.
 2. The flawdetection system set forth in claim 1 wherein said means for ratioingsaid flaw signals with said baseline signals comprises an analogmultiplier circuit coupled to said low-pass filter, an operationalamplifier coupled to said high-pass filter and said analog multipliercircuit, and means for coupling the output of said operational amplifierto the input of said analog multiplier circuit.
 3. The flaw detectionsystem set forth in claim 1 wherein said means for ratioing said flawsignals with said baseline signals comprise an analog multiplex circuitcoupled to said high-pass filter, means coupled between said low-passfilter and said analog multiplier circuit for applying the reciprocal ofsaid scan baseline signals to said analog multiplier circuit whereby theoutput of said analog multiplier circuit provides normalized flawsignals.
 4. The flaw detection system of claim 1 including a flawquantizer circuit coupled to said threshold circuit for passing anoutput indicative of a flaw only on the first occurrence of a flawsignal during a scan interval, and rejecting subsequent flaw signalsduring adjacent successive scan intervals which occur at the same scanposition.
 5. The flaw detection system of claim 4 wherein said flawquantizer circuit comprises a. an adjustable delay means coupled to saidthreshold circuit for expanding said flaw signals from said thresholdcircuit, b. scan interval delay means coupled to said adjustable delaymeans for producing a delayed flaw signal approximately one scaninterval after such flaw signal is received from said threshold circuit,and c. flaw gate means coupled to said scan interval delay means andsaid adjustable delay means for passing an output indicative of a flawonly on the first occurrence of a flaw signal during a scan interval,and rejecting subsequent flaw signals during adjacent successive scanintervals which occur at the same scan position.
 6. A flaw detectionsystem utilizing a laser scanner for detecting flaws on a surface ofmaterial, comprising a. a laser for emitting a beam of radiation, b.means for successively scanning said laser beam across a surface ofmaterial being analyzed, c. detector means for receiving radiationapPlied by said laser beam from said surface producing a signal inresponse to the intensity of the radiation applied to said detectormeans, d. threshold circuit means coupled to said detector means forproducing a flaw output signal when the signals from said detector meansexceed a predetermined level, and e. a flaw quantizer circuit coupled tosaid threshold circuit for passing an output indicative of a flaw onlyon the first occurrence of a flaw signal during a scan interval, andrejecting subsequent flaw signals during adjacent successive scanintervals which occur at the same scan position.
 7. The flaw detectionsystem set forth in claim 6 wherein said flaw quantizer circuitcomprises a. an adjustable delay means coupled to said threshold circuitfor expanding said flaw signals from said threshold circuit, b. scaninterval delay means coupled to said adjustable delay means forproducing a delayed flaw signal approximately one scan interval aftersuch flaw signal is received from said threshold circuit, and c. flawgate means coupled to said scan interval delay means and said adjustabledelay means for passing an output indicative of a flaw only on the firstoccurrence of a flaw signal during a scan interval, and rejectingsubsequent flaw signals during adjacent successive scan intervals whichoccur at the same scan position.